Vision is the primary sense utilized in driving, and is responsible for 95% of driving-related inputs.1 Age- and disease-related changes of the eye and brain may affect visual acuity, visual fields, night vision, contrast sensitivity, and other aspects of vision. External obstruction of view (eg, blepharoptosis) should not be overlooked, as it may significantly limit visual fields.

Whenever possible, vision deficits should be managed and corrected. In some situations, patients with persistent vision deficits may reduce their impact on driving safety by restricting travel to low-risk areas and conditions, such as familiar surroundings, low speed areas, non-rush hour traffic, daytime, and good weather conditions.

Section 1: Vision

Visual acuity

Please note that visual acuity licensing requirements vary from state to state. (See Chapter 8 for a state-by-state reference list of licensing requirements.) Many states require far visual acuity of 20/40 for licensure; however, recent studies indicate that there may be no basis for this requirement.2 State driver licensing agencies are urged to base their visual acuity requirements on the most current data, as appropriate.

Visual acuity may be measured with both eyes open or with best eye open, as the patient prefers. The patient should wear any corrective lenses usually worn for driving.

For best-corrected far visual acuity less than 20/70, the physician should recommend an on-road assessment performed by a driver rehabilitation specialist (where it is permitted and available) to evaluate the patient’s performance in the actual driving task.

For best-corrected far visual acuity less than 20/100, the physician should recommend that the patient not drive unless safe driving ability can be demonstrated in an on-road assessment, where permitted and available. (See also recommendations for Telescopic lenses.)

Cataracts

No restrictions if standards for visual acuity and visual fields are met, either with or without cataract removal.

Patients who require increased illumination or who experience difficulty with glare recovery should avoid driving at night and under low-light conditions, such as during storms.

Diabetic retinopathy

No restrictions if standards for visual acuity and visual fields are met.

Keratoconus

Patients with severe keratoconus correctable with hard contact lenses should drive only when the lenses are in place. If lenses cannot be tolerated, patients with severe keratoconus should not drive even if they meet standards for visual acuity, as their acuity dramatically declines outside their foveal vision, rendering their peripheral vision useless.

Macular degeneration

No restrictions if standards for visual acuity and visual fields are met.

Patients who experience difficulty with glare recovery should avoid driving at night. Patients with the neovascular “wet” form of the disease may require frequent assessment due to the rapid progression of the disease.

Nystagmus

No restrictions if standards for visual acuity and visual fields are met.

Telescopic lens

A bioptic telescope is an optical telescope mounted on the lens of eyeglasses. During normal use, the wearer can view the environment through the regular lens. When extra magnification is needed, a slight downward tilt of the head brings the object of interest into the view of the telescope.3 The specialist who prescribes a telescopic lens should ensure that the patient is properly trained in its use.

It has not been established whether telescopes enhance the safety of low-vision drivers. As stated in the American Academy of Ophthalmology’s Policy Statement, Vision Requirements for Driving:

“More than half the states allow drivers to use bioptic telescopes mounted on glasses, through which they spot traffic lights and highway signs. It has not yet been demonstrated whether the estimated 2,500 bioptic drivers in the United States drive more safely with their telescopes than they would without them. The ability to drive safely using bioptic telescopes should be demonstrated in a road test in all cases.”2

Please note that licensing requirements regarding the use of bioptic telescopes vary from state to state. A road test should be administered only in those states that permit the use of bioptic telescopes in driving.

Visual field

While it is acknowledged that an adequate visual field is important for safe driving, there is no conclusive evidence to define what is meant by “adequate.” As a result, visual field requirements vary between states, with many states requiring a visual field of 100 degrees or more along the horizontal plane, and other states having a lesser requirement or none at all.3 (See Chapter 8 for a state-by-state reference list of visual field requirements.)

If the primary care physician has any reason to suspect a visual field deficit (eg, through patient report, medical history, or confrontation testing), he/she should refer the patient to an ophthalmologist or optometrist for further evaluation. The primary care physician and specialist should be aware of their particular state’s visual field requirements, if any, and adhere to them.

For binocular visual field at or near the state minimum requirement or of questionable adequacy (as deemed by clinical judgment), a driver evaluation (including on-road assessment) performed by a driver rehabilitation specialist is strongly recommended. Through driving rehabilitation, the patient may learn to compensate for decreased visual fields. In addition, the driver rehabilitation specialist may prescribe enlarged side and rear view mirrors as needed and train the patient in their use.

Glaucoma

No restrictions if standards for visual acuity and visual fields are met.

Hemianopia/
quadrantanopia

The physician may choose to refer the patient to a driver rehabilitation specialist for assessment and rehabilitation. With or without rehabilitation, the patient should drive only if he/she demonstrates safe driving ability in an on-road assessment performed by a driver rehabilitation specialist.

Please note that licensing requirements regarding hemianopia and quadrantanopia vary from state to state. A road test should be administered only in those states that do not prohibit individuals with hemianopia or quadrantanopia from driving.

Monocular vision

Patients with acquired monocularity may need time to adjust to the lack of depth perception and reduction in total visual field. This period of adjustment varies between individuals, but it is reasonable to recommend temporary driving cessation for several weeks.

Following this period, there are no restrictions if standards for visual acuity and visual fields are met. Upon resumption of driving, patients should be advised to assess their comfort level by driving in familiar, traffic-free areas before advancing to heavy traffic.

Ptosis

Individuals with fixed ptosis may drive without restrictions if their eyelids do not obscure the visual axis of either eye, and they are able to meet standards for visual acuity and visual fields without holding their head in an extreme position.

Retinitis pigmentosa

No restrictions if standards for visual acuity and visual fields are met. Patients who require increased illumination or who experience difficulty adapting to changes in light should not drive at night or under low-light conditions, such as during storms.

Contrast sensitivity

Contrast sensitivity is a measure of an individual’s ability to perceive visual stimuli that differ in contrast and spatial frequency. Contrast sensitivity tends to decline with age; accordingly, deficits in contrast sensitivity are much greater in older individuals compared to their younger counterparts.4

Among older drivers, binocular measures of contrast sensitivity have been found to be a valid predictor of crash risk. However, there are presently no standardized cut-off points for contrast sensitivity and safe driving, and it is not routinely measured in eye exams.

Due to its usefulness in predicting crash risk, it is strongly recommended that standardized contrast sensitivity scales be developed, validated, and utilized in the clinical and driver licensing settings.

Defective color vision

No restrictions if standards for visual acuity and visual fields are met.

Deficits in color vision are common (especially in the male population) and usually mild. In an extensive review of the literature on color vision and driving, the majority of studies found no association between color vision deficits and increased crash rates.5 Only 19 states require prospective drivers to undergo color vision screening, and most of these states require screening for commercial drivers only.3

Despite reported difficulties with color vision discrimination while driving (eg, difficulty distinguishing the color of traffic signals, confusing traffic lights with street lights, and difficulty detecting brake lights), it is unlikely that color vision impairments represent a driving hazard.4 With the standardization of traffic signal positions, color blind individuals are able to interpret traffic signals correctly because they can identify the traffic signal by its position. Physicians may wish to advise patients that the order of signals in the less commonly used horizontal placement is (from left to right) red, yellow, green.

Poor night vision

If the patient reports poor visibility at night, the physician should recommend optometric and/or ophthalmologic evaluation. If the evaluation does not reveal a treatable cause for poor night vision, the physician should recommend that the patient not drive at night or under other low-light conditions, such as during storms.